In recent years, legal scholars have utilized the science of implicit social cognition to reveal how unconscious biases affect perceptions, behaviors, and judgments. Employing this science, scholars critique legal doctrine and challenge courts to take accurate theories of human behavior into account or to explain their failure to do so. Largely absent from this important conversation, however, are Fourth Amendment scholars. This void is surprising because the lessons of implicit social cognition can contribute much to understanding police behavior, especially as it relates to arrest efficiency or hit rates - the rates at which police find evidence of criminal activity when they conduct a stop and frisk. Empirical evidence consistently demonstrates that the police disproportionately stop and frisk non-Whites although stops and searches of Whites are often more successful in yielding evidence of criminal activity. While economists and criminal process scholars both suggest that arrest inefficiency is due to conscious racial bias, the science reveals that unconscious biases may also contribute to this inefficient policing. This Article argues that taking account of the science of implicit social cognition is important to the study of Fourth Amendment jurisprudence and policing. It demonstrates that the failure to recognize the effects of implicit bias has resulted in a Fourth Amendment legal regime that unintentionally exacerbates inefficient policing by strengthening the effects of implicit bias on police behavior. The Article suggests doctrinal and structural changes to ameliorate inefficient policing and more effectively protect privacy against arbitrary government intrusion.